The present invention relates to a tire with radial carcass reinforcement, and more particularly to a xe2x80x9cheavy-vehiclexe2x80x9d tire, intended to be fitted on vehicles such as lorries, road tractors, buses, trailers and others, and in which a novel reinforcement structure for the beads is adapted to improve the life of said beads.
Generally, a tire of the type in question comprises a carcass reinforcement formed of at least one ply of metal cables, which is anchored in each bead to at least one bead wire, forming an upturn. The carcass reinforcement is radially surmounted by a crown reinforcement, composed of at least two plies of metal cables, crossed from one ply to the next and forming angles of between 10xc2x0 and 45xc2x0 with the circumferential direction. The carcass reinforcement upturns are generally reinforced by at least one ply of metal cables oriented at a small angle relative to the circumferential direction.
In the case of the presence of a single bead reinforcement ply, the latter may be located along the carcass reinforcement upturn with a radially upper end located above or below the radially upper end of the carcass reinforcement upturn. As for the radially lower end of such a ply, it is generally located either on a straight line parallel to the axis of rotation and passing approximately through the center of gravity of the meridian section of the anchoring bead wire of the carcass reinforcement, in the case of a tire having beads intended to be mounted on rim seats inclined at 15xc2x0xc2x12xc2x0, or on a straight line parallel to the axis of rotation and passing through a point located between the center of gravity of the meridian section of the anchoring bead wire and the point of maximum axial width of the carcass reinforcement, in the case of a tire having beads intended to be mounted on rim seats inclined at 0xc2x0 or at 5xc2x0xc2x11xc2x0. In this second case, the bead reinforcement ply is then wound around the bead wire, so as to have an axially outer strand and an axially inner strand, the radially upper end of the axially inner strand being generally located beneath the radially upper end of the axially outer strand.
Furthermore, the life of xe2x80x9cheavy-vehiclexe2x80x9d tires, owing to the progress achieved, and to the fact that certain types of travel are made less of a handicap as far as wear of the tread is concerned, has become such that it is also necessary to improve the life of the beads, and more particularly of tires subject to prolonged travel, this travel frequently inducing a high temperature of the beads owing to the temperatures reached by the mounting rims.
Numerous solutions have been described for improving the life of the beads of tires, whether they are intended to be mounted on 15xc2x0-seat rims or flat rims or 5xc2x0-seat rims: for example, it has been proposed to replace the metallic reinforcement ply by a plurality of plies of reinforcement elements, textile ones, for example, crossed from one ply to the next and said plies being located axially either on the same side of the upturn or on either side of said upturn, or alternatively partly along the upturn and partly along the carcass reinforcement.
The life of the beads can also be improved by arranging two reinforcement plies along the carcass reinforcement, without reinforcement of the upturn.
From reading French application FR 2 730 190, said improvement can be obtained by the presence in the beads of at least one reinforcement ply formed of circumferential metallic elements, which ply is wound around the bead wire on the outside of the wound part of the carcass reinforcement, such that the radially upper ends respectively of the axially outer strand and of the axially inner strand are radially located above a straight line parallel to the axis of rotation and passing through the point of the bead wire which is farthest from said axis of rotation. The carcass reinforcement, formed of radial cords or cables, is thus formed, at the level of its contact surface with the bead wire, as is known, of substantially circumferential elements which are generally metallic in the form of wound cords, cables, bands or strips, inserted between said elements with substantially circumferential orientation and the additional ply of metallic elements, which are also circumferential. This structure thus makes it possible to take up the tensile stresses to which the carcass reinforcement is subjected, and thus minimizes all the deformations at the ends of the carcass reinforcement upturn, whatever the traveling conditions.
The solution of a bead reinforcement ply with circumferential reinforcement elements does not appear to be the technically and industrially optimal solution for tires having beads intended to be mounted on so-called flat rims or rims having seats inclined at 5xc2x0, since the important factor does not seem to be the presence of circumferential elements.
Furthermore, and with the aim of lightening tires for heavy vehicles which are mounted on rims having seats inclined at 0xc2x0 or 5xc2x0xc2x11xc2x0, numerous attempts have been made to dispense with the axially inner strand of the reinforcement ply of the bead, and to have substantially the same architecture of carcass reinforcement and reinforcement ply for the two types of rims used.
Although said known solutions, the object of which is to avoid deradialization of the cables of the upturn of the carcass reinforcement and to minimize the radial and circumferential deformations to which the end of said upturn and the radially upper end of the reinforcement ply are subjected, respectively, have improved the life of the bead reinforcements, the performance of the tires mounted on rims having 0xc2x0 seats or 5xc2x0xc2x11xc2x0 seats is on the other hand reduced by the appearance and propagation of breaks in the outer layer of rubber covering the bead and providing the connection to the rim.
The invention proposes to overcome the above disadvantages.
In order to improve the life of a tire required to bear heavy loads and having beads intended to be mounted on flat rim seats or rim seats which are inclined at 5xc2x0, said tire according to the invention, comprising at least one radial carcass reinforcement, formed of at least one ply of inextensible reinforcement elements and anchored in each bead to a bead wire to form an upturn, the end of which is located at a radial distance HRNC from the base of the bead, each bead being reinforced by at least two additional reinforcement armatures, at least one first armature formed of at least one ply of radial reinforcement elements and at least one second armature formed of at least one ply of inextensible elements forming an angle xcex1 with the circumferential direction such that 0xc2x0 less than xcex1 less than 45xc2x0, characterized in that, viewed in meridian section, the first reinforcement armature is formed of radial textile reinforcement elements not wound around the anchoring bead wire of the carcass reinforcement and located axially to the outside of the second reinforcement, the radially inner end of said first reinforcement being located between the two straight lines parallel to the axis of rotation and passing respectively through the points of the anchoring bead wire which are respectively farthest and least far from the axis of rotation, the radially outer end being located at a distance HLE from the base of the bead of between 80% and 120% of the distance HRNC, whereas the second armature, which is not wound around said anchoring bead wire, has a radially inner end located between the straight line parallel to the axis of rotation and the base of the bead and a radially outer end at a distance HR from said base of between 60% and 75% of HRNC.
Reinforcement elements will be considered to be radial if the angle which they form with the circumferential direction of the tire lies within a range of 80xc2x0-100xc2x0.
Likewise, in the spirit of the invention, xe2x80x9cradially upper endxe2x80x9d of a bead reinforcement armature which may be formed of one or more plies is to be understood to mean the end of the reinforcement ply which is farthest from the axis of rotation, the reinforcement plies possibly having upper ends included in a range of radial distance of at most 20 mm. Likewise, the radially lower end of a bead reinforcement armature will be the lower end of the ply least far from the axis of rotation.
The first armature of radial reinforcement elements is advantageously formed of a single ply of aliphatic polyamide textile cables composed of two plied cords, at least 250/250 twists per meter. It is preferably separated from the second armature by a profiled element of rubber mix of a thickness of at least 2 mm.
The second additional bead reinforcement armature may be formed of at least one ply of circumferential metallic reinforcement elements; in this case, it is advantageous, in order to facilitate manufacture and to reduce the cost thereof, to select as reinforcement elements for said ply lengths or assemblies of lengths of metal cables, of a circumferential length less than the circumferential length of the center axis of the bead wire. It may also be formed, as known per se, of a single ply of metal cables parallel to each other in the ply and forming a small angle of between 5xc2x0 and 30xc2x0 with the circumferential direction. In all cases, it is preferably separated from the carcass reinforcement upturn by a profiled element of rubber mix of a thickness of at most 3 mm.